This invention relates to an air pump, especially a diaphragm air pump, for use in a purifying system of exhaust gas for a motor vehicle.
Conventional rotary air pumps for use in purifying systems of exhaust gas are actuated by crankshafts or other shafts of the engines. Thus, the output of this type of air pump increases proportionally to the increase of revolutions of the crankshaft of the engine. However, secondary air from the air pump should be supplied to the purifying system for example to a thermal reactor at low or middle revolutions of the engine of the vehicle, but not so necessarily to be supplied at high revolutions thereof. In the conventional air pump, there is a main problem that the output of the pump is specially low at the low revolutions of the engine, so that it is necessary to use an air pump of large volume to operate perfectly the purifying system at the low revolutions. Also, in a diaphragm air pump in which a diaphragm is actuated through without use of resilient means, there is a problem in durability of the diaphragm, in addition to the above drawback, since frequency of oscillations and inertia force of the diaphragm increase proportionally to the increase of revolutions of the crankshaft.